The provision of safe and clean water that is also visually attractive to the user is important in municipal, industrial, and recreational applications. Conventional water treatments employ physical, chemical, and biological processes either alone or in combination to produce water of acceptable quality.
In applications where water is intended for human contact or consumption, the water must be treated so that it is aesthetically pleasing in terms of taste, color, turbidity, odor, and pH, environmentally safe, and effectively free of pathogens and chemicals responsible for both acute and chronic illness. Conventional methods use chemicals as oxidizers, biocides, algaecides, and pH buffers for the treatment of water. Typically, the chemicals are added to the water separately as part of an overall water maintenance or purification program. The water is monitored on an hourly, daily, or weekly basis, and when a particular treatment parameter is not acceptable or in compliance with regulatory levels, the appropriate amount of the necessary chemical is added. Often, treatment of one water quality parameter causes another water quality parameter to change. Conventional treatment, therefore, employs a continuous balancing process of monitoring water quality parameters and dosing with various chemicals to create and to maintain the appropriate water quality.
It must be appreciated that potable water typically has a pH of 8.3 with a total alkalinity of 50 ppm and a calcium content of 100 ppm. The term “total alkalinity” is used to describe the total amount of dissolved alkaline substances in water, excluding calcium. “Dissolved solids” in suspension in swimming pool water, predominantly provided by the total alkalinity and calcium in the water, give the water its “blue” color when sunlight reflects off the water. Thus, reductions in the amount of dissolved solids in water will result in the water having an increasingly green color. It will be appreciated that it is desirable to provide a water purification composition that provides sufficient dissolved solids to give the water a blue color.
In applications such as swimming pools and spas, chemical combinations attempt to provide a complete water quality treatment. For example, U.S. Pat. No. 5,700,377, issued to Cox on Dec. 23, 1997, discloses a complete treatment for the purification of water in non-porous swimming pools, obviating the need for the addition of any other compounds to the water. The chemical composition of Cox includes a peroxide compound, an ammonium-based biocidal compound, an acidic compound, a basic compound, a calcium-releasing basic compound, and EDTA in the form of a “kit” or mixture. The composition is added to the water when the pH of that water is outside the human comfort zone of 7.2 to 7.6 in order to bring the pH within the zone range. Therefore, water clarification is combined with a pH adjustment. However, the use of such mixtures exposes the user to the disadvantage of maintaining the mixture in a condition that prohibits the reaction of the basic material with the acidic materials. Also, such reaction occurs upon addition of the mixture to the water being treated.
Attempts to combine various chemicals into a convenient tablet form have been known. Tabletting of various chemicals for release at various times has been used extensively in the administration of medicine. Typical examples of such tablets are found in U.S. Pat. No. 6,183,778 issued to Conte et al. on Feb. 6, 2001; U.S. Pat. No. 6,149,940 issued to Maggi et al. on Nov. 21, 2000; U.S. Pat. No. 6,136,344 issued to Depui et al. on Oct. 24, 2000; and U.S. Pat. No. 6,083,533 issued to Cremer on Jul. 4, 2000. It can be appreciated that time release of medicaments has great value in treatment regimens and tablets that provide such properties are numerous. The above list is a mere sample of those references wherein tablets contain various layers having different solubility rates in digestive fluids.
Another industry finding great utility with multi-layered tablets having various components for differing purposes is the automatic dishwashing detergent industry. There, the advantage of various wash cycles of automatic dishwashers provide an opportunity to build a multi-layer tablet wherein several agents are combined in a layered fashion to supply the appropriate cleaning chemical at the propitious time in the wash cycle. A typical example of such disclosures are U.S. Pat. No. 6,194,368, issued to Waschenbach et al. on Feb. 27, 2001, wherein the first layer of a dishwashing detergent tablet contains an activated, halogen-free bleach, and silver/copper corrosion inhibitor in an outer layer and a bleach activator in another layer. U.S. Pat. No. 5,962,387, issued to Gorlin et al. on Oct. 5, 1999, discloses a three-layer tablet wherein each layer contains a different detergent formulation. As the wash cycle proceeds, a different formulation believed optimum for each portion of the cycle is exposed. In U.S. Pat. No. 5,837,663, issued to Nicholson et al. on Nov. 17, 1998, there is disclosed a two-layer tablet for automatic dish washing where a first layer contains a buffer, a builder and an enzyme which dissolves at a pH of 9-11. A second layer is provided containing a peracid and an acidity agent having a melting point of from 35 to 50 degrees C. along with a carrier. The second layer delivers a pH of from 6.5-9. The release order is said to allow optimum removal of stains and food from the dishes. Another example of a multi-layer tablet for use in automatic dishwashers allowing for different pH levels during a single wash cycle appears in U.S. Pat. No. 5,783,540, issued to Secemski et al. on Jul. 21, 1998. In this patent, an oxygen bleach, a buffer system to deliver a pH of 8.5-11, a builder and an enzyme are contained in one layer while a second layer is provided containing an acidity agent to provide a pH below 9, a carrier having a high melting point for the acidity agent and an anti-scaling agent. In theory, the high melting carrier is dispersed in the high temperature final rinse cycle thereby providing a superior finish to the articles, especially glass. Other examples of multi-layer tablets used in automatic dish washing machines are found in U.S. Pat. No. 5,549,913 issued to Colombo et al. on Aug. 27, 1996; U.S. Pat. No. 5,133,892 issued to Chun et al. on Jul. 28, 1992; and U.S. Pat. No. 4,828,745 issued to Jeschke et al. on May 9, 1989.
The use of tablets for administering halogen-containing chemicals to swimming pools has long been known. Usually the tablets are placed in the pool water system at points where flowing water is provided such as in the filtration system skimmer or in a floating basket at the surface of the pool. As noted above, in most instances, the condition of the pool water is monitored periodically to insure a desirable pH level, as well as desirable algaecide, alkalinity, and hardness control is maintained while administering a generally acid contributing halogen containing compound. A two-layer tablet for chlorination of water systems is disclosed in U.S. Pat. No. 3,873,685 issued to Kibbel, Jr. et al. on Mar. 25, 1975. This patent discloses the combination of contiguous layers in one tablet wherein one layer contains a fast dissolving halogen-releasing agent while a second layer provides a slower dissolving halogen-releasing agent. A relatively fast dissolving halogen-releasing agent, sodium dichloroisocyanurate dihydrate is contained in one discrete layer and trichloroisocyanuric acid is contained in another layer. Various geometric shapes of tablets are suggested wherein the discrete portions of the ingredients are provided in structures having either a layered structure or an inner core and outer core such as in the shape of a rod or oval ball. While providing a measure of convenience in placing halogen-releasing materials in the water, the need still arises to monitor and control the total alkalinity of the water as well as the pH level, particularly in swimming pools.
Because of the proximity of reactive chemicals such as an acidic material and a basic material to each other is a single composition, the production of such products have proven to have limited or no commercial value because of the danger presented by the possibility of an exothermic reaction occurring during storage and shipping of large quantities of such materials.